1. Field of the Disclosure
The disclosure relates to a level conversion circuit and a method for converting voltage level thereof, and particularly to a level conversion circuit having self-bias control and a method for converting voltage level thereof.
2. Description of Related Art
Conventional level conversion circuits employ a multilevel level shifter to covert an input signal into a negative power domain from a positive power domain. Then, an output signal is outputted to a circuit to be controlled at the next stage. Here, the positive power domain is, for example, a power segment from a positive operation voltage to a ground voltage; the negative power domain is, for example, a power segment from a ground voltage to a negative operation voltage. However, in conventional application where the level conversion circuit operates when the positive power domain is converted into the negative power domain, since an electronic device within the level conversion circuit has a withstanding voltage limit for operation, that is, the difference between the maximum voltage and minimum voltage of the electronic device which operates in the power domain thereof shall not be greater than a rated voltage value, the number of required operation voltage externally supplied to the level shifter during operation needs to be taken into consideration. Meanwhile, in a power on/off procedure, the operation voltage has to be capable of accurately outputting a control signal and ensures there is no incorrect level output that causes the controlled circuit to be abnormal. In the example, if the electronic device within the level conversion circuit is a middle voltage device, a withstanding voltage limit thereof is approximately 6 volt; if it is a high voltage device, a withstanding voltage limit thereof is approximately 12 volt.
Based on the aforementioned concept, the design of a conventional level conversion circuit may be realized by the following two methods; one of which is to employ a middle voltage device within the level conversion circuit with the addition of a plurality of external voltages provided by an external circuit, wherein the external voltages includes a higher negative voltage and a lower negative voltage. In the power on/off procedure, the design of the two negative voltages is in a certain sequence so as to prevent the level shifter from outputting an incorrect level to the next stage circuit to cause abnormal current. The other method is to use a high voltage device additionally to design the level conversion circuit; however, the design requires two devices, which leads to increased costs and time needed for manufacturing process.